Refactored Classifier to an sklearn estimator

[OmriKaduri]

Hey,

I've wanted to use your classifier for a multiclass problem. The easiest way I've thought about is using sklearn OneVsRestClassifier and refactoring your Classifier to be an sklearn estimator (by using inheritance from BaseEstimator and ClassifierMixin). Also, I've added predict_proba function.

So I've thought it would be nice to open a PR for anyone want to use this classifier for multiclass problems 😃